1. Field of the Invention
The present general inventive concept relates to a method of and apparatus to enhance low-frequency components and medium-frequency components of an audio signal.
2. Description of the Related Art
A small-size speaker mounted in a portable device such as a notebook personal computer (PC) or an MP3 player has a difficulty in fully reproducing low-frequency components of an audio signal due to its physical limit, i.e., its small size. Such a difficulty may cause distortion of sound quality.
FIG. 1 illustrates a conventional low-frequency enhancing apparatus.
Referring to FIG. 1, the conventional low-frequency enhancing apparatus includes a low-pass filter 110, an SIN function generation module 122, a COS function generation module 124, a band-pass filter 130, and a mixer 140.
Upon input of an audio signal, the low-pass filter 110 performs low-pass filtering on the audio signal input for each channel in order to extract only low-frequency components (e.g., less than 120 Hz).
The SIN function generation module 122 and the COS function generation module 124 modulate low-pass filtered signals in order to generate harmonic-frequency signals.
The band-pass filter 130 performs band-pass filtering on signals transformed to an SIN function and a COS function in order to extract only harmonic-frequency signals of a predetermined order.
The mixer 140 mixes the harmonic-frequency signals filtered by the band-pass filter 130 with the input audio signal, thereby generating an audio signal having enhanced low-frequency components for each channel.
Enhancement of low-frequency components using harmonic-frequency signals uses an acoustic effect in which human ears perceive the tone of a frequency that is a multiple of a fundamental frequency as the tone of the fundamental frequency.
FIG. 2 is a view illustrating ideal harmonic-frequency signals for frequency component enhancement.
Referring to FIG. 2, a 220 Hz fundamental-frequency component and harmonic-frequency signals are illustrated. When the fundamental-frequency component is at 220 Hz as illustrated in FIG. 2, harmonic-frequency signals having frequencies that are multiples of 220 Hz, i.e., harmonic-frequency signals having 440 Hz, 660 Hz, and 880 Hz are ideal harmonic-frequency signals for frequency component enhancement. Accordingly, as the frequencies of the ideal harmonic-frequency signals increase, the amplitudes of the ideal harmonic-frequency signals decrease as illustrated in FIG. 2.
If a user hears the tones of the ideal harmonic-frequency signals, the user perceives the tones as the tone of the 220 Hz fundamental-frequency component. Thus, by using the harmonic-frequency signals, it is perceived as if the intensity of sound having a tone corresponding to 220 Hz is enhanced.
However, according to the conventional low-frequency component enhancing apparatus illustrated in FIG. 1, the amplitudes of harmonic-frequency signals do not decrease as the frequencies of the harmonic-frequency signals increase as with the ideal harmonic-frequency signals illustrated in FIG. 2. Instead, the amplitudes of harmonic-frequency signals are constant over different frequencies and distortion is caused in tones when the harmonic-frequency signals are mixed with the original audio signal.
According to a conventional medium-frequency component enhancing method, intensity of energy of an audio signal in a medium-frequency band is increased using an equalizer, causing distortion in the tone of the audio signal.
Accordingly, the conventional low-frequency component enhancing method and the conventional medium-frequency component enhancing method cause a significant change in a tone during enhancement of low-frequency components and medium-frequency components.